UPDATE: On Saturday, the Human Rights Campaign revoked its endorsement of Sen. Mark Kirk and switched its support to Rep. Tammy Duckworth, after a vote by its leadership. For details, click here.

After a tweet by the Human Rights Campaign calling on Republican Sen. Mark Kirk to apologize for mocking his Democratic opponent, Rep. Tammy Duckworth, her immigrant background and her family’s history of military service, Kirk did just that, with a tweet of his own,

In a Twitter post Friday, Kirk wrote: “Sincere apologies to an American hero, Tammy Duckworth, and gratitude for her family’s service.”

The apology comes the morning after their Senate debate Thursday in Springfield, Ill., in a race that is unusual in itself in that both candidates are disabled. Duckworth spoke proudly of how her family has “served this nation in uniform going back to the Revolution.”

Kirk quipped he had “forgotten (that her) parents came all of the way from Thailand to serve George Washington.” Watch the clip below from NBC News:

Duckworth, a native of Thailand, has a mother of Chinese descent and a father who first went to Southeast Asia to serve with the U.S. Marines in Vietnam. It is he who traces his heritage to the Revolutionary War, as revealed in a 2002 profile in Mother Jones.

AP Photo/Seth Perlman

Kirk suffered a massive stroke in 2012, and often uses a wheelchair or crutches to get around. Duckworth, herself a veteran who lost both legs serving her nation in Iraq, tweeted this photo of her mother and father following the debate:

The Democratic Senatorial Campaign Committee immediately called Kirk’s comments “wrong and racist.” But many tweets from within the LGBTQ community centered on the silence from HRC, which raised eyebrows in the first place by endorsing the Republican candidate, Kirk.

In March, HRC president Chad Griffin said in a statement, “Whether it was becoming the first Republican Senator to co-sponsor the Equality Act, co-sponsoring a bill to help schools combat anti-LGBT bullying or supporting marriage equality, Senator Kirk has demonstrated time and again that he believes in full federal equality.”

And Friday morning, Brandon Lorenz tweeted this in response to the news that HRC would stand by its endorsement:

The twitterverse was not kind to HRC, with some promoting a petition:

HRC was offered an opportunity to comment for this report but directed us instead to Brandon Lorenz’s tweet.